The present invention is related to a method of manufacturing porous magnesia clinkers which are light in weight and have a high heat insulating property and an excellent product strength.
Basic refractory materials made mainly of magnesia clinkers are generally used as an essential lining material in most of the industrial kilns in the fields of steel making and the ceramic industry. This is because magnesia clinkers have excellent properties as basic refractory material; they have a high melting point of 2,800.degree. C., a low tendency for slaking because of their comparatively high chemical inertness, and a corrosion resistance against basic slug which is remarkably higher than that of the other materials such as alumina and mullite. However, they are defective in that their heat conductivity is high. If magnesia clinkers could be made porous, the heat conductivity can be reduced.
There have been known in the prior art following manufacturing methods for porous magnesia clinkers:
(i) A method of adding sawdust, polystyrene, etc. to the raw material, forming and firing the same. PA0 (ii) A method of adding foam in magnesia powder slurry before drying and firing. PA0 (iii) A method of adding Al powder or acetic acid in magnesia powder slurry before forming and firing. PA0 (iv) A method of electrically melting magnesia clinkers and blowing compressed air to obtain bubbles.
However, all of the above mentioned methods are defective in that the strength of formed products or calcined products are extremely low. Further, the fields of application is extremely limited for the products prepared by the method (iv) as electrical melting method results in a remarkably high product cost.